Immunohistochemical distribution of pro-somatostatin-related peptides in hippocampus

Blockade of excitation reveals inhibition of dentate spiny hilar neurons recorded in rat hippocampal slices

1. Extracellular and intracellular recordings in rat hippocampal slices were used to compare the synaptic responses to perforant path stimulation of granule cells of the dentate gyrus, spiny "mossy" cells of the hilus, and area CA3c pyramidal cells of hippocampus. Specifically, we asked whether aspects of the local circuitry could explain the relative vulnerability of spiny hilar neurons to various insults to the hippocampus. 2. Spiny hilar cells demonstrated a surprising lack of inhibition after perforant path activation, despite robust paired-pulse inhibition and inhibitory postsynaptic potentials (IPSPs) in adjacent granule cells and area CA3c pyramidal cells in response to the same stimulus in the same slice. However, when the slice was perfused with excitatory amino acid antagonists [6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), or CNQX with 2-amino-5-phosphonovaleric acid (APV)], IPSPs could be observed in spiny hilar cells in response to perforant path stimulation. 3. The IPSPs evoked in spiny hilar cells in the presence of CNQX were similar in their reversal potentials and bicuculline sensitivity to IPSPs recorded in dentate granule cells or hippocampal pyramidal cells in the absence of CNQX. 4. These results demonstrate that, at least in slices, perforant path stimulation of spiny hilar cells is primarily excitatory and, when excitation is blocked, underlying inhibition can be revealed. This contrasts to the situation for dentate and hippocampal principal cells, which are ordinarily dominated by inhibition, and only when inhibition is compromised can the full extent of excitation be appreciated.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in gamma-aminobutyric acid and somatostatin in epileptic cortex associated with low-grade gliomas

✓ The role of specific neuronal populations in epileptic foci was studied by comparing epileptic and nonepileptic cortex removed from patients with low-grade gliomas. Epileptic and nearby (within 1 to 2 cm) nonepileptic temporal lobe neocortex was identified using electrocorticography. Cortical specimens taken from four patients identified as epileptic and nonepileptic were all void of tumor infiltration. Somatostatin- and γ-aminobutyric acid (GABAergic)-immunoreactive neurons were identified and counted. Although there was no significant difference in the overall cell count, the authors found a significant decrease in both somatostatin- and GABAergic-immunoreactive neurons (74% and 51 %, respectively) in the epileptic cortex compared to that in nonepileptic cortex from the same patient. It is suggested that these findings demonstrate changes in neuronal subpopulations that may account for the onset and propagation of epileptiform activity in patients with low-grade gliomas.

Pattern of neuronal death in the rat hippocampus after status epilepticus. Relationship to calcium binding protein content and ischemic vulnerability

The pattern of hippocampal cell death has been studied following hippocampal seizure activity and status epilepticus induced by 110-min stimulation of the perforant pathway in awake rats. The order of vulnerability of principal cells in the different hippocampal subfields--as determined by silver impregnation--was found to be very similar to the pattern found in ischemia; i.e., dentate hilus greater than CA1, subiculum greater than CA3c greater than CA3a,b greater than dentate granule cells. The hilar somatostatin-containing cells were the most vulnerable cell type, whereas all other subpopulations of nonprincipal neurons--visualized by immunocytochemistry for the calcium binding proteins parvalbumin and calbindin--were remarkably resistant. Pyramidal cells in the CA3 region containing neither of the examined calcium binding proteins were more resistant to overexcitation than CA1 pyramidal cells, most of which do contain calbindin. This indicates that no simple relationship exists between vulnerability in status epilepticus and neuronal calcium binding protein content, and that local and/or systemic hypoxia during status epilepticus may be responsible for the ischemic pattern of cell death.

Somatostatin and neuropeptide Y in organotypic slice cultures of the rat hippocampus: An immunocytochemical and in situ hybridization study

The neuronal distributions of somatostatin and neuropeptide Y and their respective mRNAs in hippocampal slice cultures were examined by immunohistochemical staining and in situ hybridization. For the in situ hybridization we used an alkaline phosphatase-labelled oligodeoxynucleotide probe for somatostatin mRNA and an 35S-labelled oligodeoxynucleotide probe for neuropeptide Y mRNA. For both neuropeptides the immunostained and hybridized neurons displayed a comparable, organotypic distribution. Most labelled neurons were located in the dentate hilus and stratum oriens of CA3 and CA1. Additional neurons were found in stratum radiatum and pyramidale of CA3, but very few in the corresponding layers of CA1. In all locations the density of somatostatin- and neuropeptide Y-reactive cells exceeded that observed in vivo. Also, the hybridization signal of the individual neurons appeared enhanced in the slice cultures. Methodologically it was noted that the non-radioactive alkaline phosphatase-labelled oligodeoxynucleotide probe gave excellent in situ hybridization results with detailed cellular resolution and no apparent problems of tissue penetration, even when used on whole-mount explants. These results demonstrate that somatostatin and neuropeptide Y-immunoreactive and mRNA containing neurons retain their organotypic distribution and basic morphological characteristics in the slice cultures. The supernormal density of these neurons and their hybridization signals indicate that a transient developmental increase in neuropeptide expression may persist in vitro.

Direct observation of the agonist-specific regional vulnerability to glutamate, NMDA, and kainate neurotoxicity in organotypic hippocampal cultures

Excessive activation of excitatory amino acid receptors has been implicated in the neuronal degeneration caused by ischemia, hypoglycemia, and prolonged seizures. We have observed directly the time course and regional vulnerability of hippocampal neurons to glutamate receptor-mediated injury in organotypic hippocampal cultures, a preparation which combines accessibility and long-term survival with preservation of regional differentiation and neuroanatomic organization. Cultures were incubated with the fluorescent dye propidium iodide which selectively enters and stains cells only after membrane damage. After 5 to 10 min of a 30-min exposure to kainate (100 microM), large neurons in the hilus of the dentate were first to become brightly fluorescent. Propidium staining subsequently appeared in the other regions of the hippocampus and increased to a maximum over the first 6 h of recovery. NMDA (10 microM) caused propidium staining that was limited to CA1 and the dentate gyrus of the cultures, sparing CA3, consistent with the regions of highest NMDA receptor density in vivo. Glutamate (1 mM) caused a delayed, progressive pattern of staining that began in CA1 (2 to 4 h after exposure), then extended to include CA3 and finally the dentate gyrus over the next 24 h. Release of LDH activity into the media was slower and less sensitive than propidium staining. Histologic degeneration was limited to neurons 24 h after agonist exposure and was consistent with the propidium staining. NMDA, kainate, and glutamate each produced a unique pattern of neuronal injury. Most notably, glutamate had low potency as a toxin and its pattern of neuronal injury was not reproduced by NMDA.

Somatostatin-28 (1-12)-like immunoreactivity in the cat diencephalon

Using an indirect immunoperoxidase technique, the location of somatostatin-28 (1-12)-like immunoreactive fibres and cell bodies in the cat diencephalon was studied. The hypothalamus was richer in somatostatin-28 (1-12)-like immunoreactive structures than the thalamus. A high density of immunoreactive fibres was observed in the nuclei habenularis lateralis, paraventricularis anterior (its caudal part), filiformis, hypothalami ventromedialis, and regio praeoptica, whereas a moderate density was found in the nuclei paracentralis, supraopticus, supra chiasmaticus, hypothalamus posterior and area hypothalamica dorsalis. The nuclei lateralis dorsalis, lateralis posterior, medialis dorsalis, rhomboidens, centralis medialis, ventralis medialis, reuniens, anterior dorsalis, parataenialis, interanteromedialis, hypothalamus lateralis, hypothalamus dorsomedialis and arcuatus had the lowest density of immunoreactive fibres. In addition, a high or moderate density of somatostatin-28 (1-12)-like immunoreactive cell bodies was observed in the nuclei paraventricularis hypothalami, supraopticus, supra chiasmaticus, area hypothalamics dorsalis, subparafascicularis, hypothalamus posterior and hypothalamus anterior, whereas scarce immunoreactive perikarya were visualized in the nuclei lateralis dorsalis and parafascicularis. The distribution of somatostatin-28 (1-12)-like immunoreactive structures is compared with the location of other neuropeptides in the cat diencephalon.

Coexistence of muscarinic acetylcholine receptors and somatostatin in nonpyramidal neurons of the rat dorsal hippocampus

This study describes the colocalization of muscarinic acetylcholine receptors (mAChRs) and the neuropeptide somatostatin (SOM) in nonpyramidal neurons of the rat dorsal hippocampus. SOM and mAChRs were identified by immunocytochemistry employing antibody S309 and M35, respectively. Half of the SOMergic cell population is found to be immunoreactive for muscarinic receptor protein as obtained by fluorescent double-labeling techniques. These findings provide additional evidence for a direct cholinergic influence upon SOMergic, nonpyramidal neurons, and defines the anatomical distribution of SOMergic, cholinoceptive neurons in the dorsal hippocampus. Concerning the muscarinic cholinoceptive, nonpyramidal neuron population of the dorsal hippocampus, a considerable number (approximately one-third) was found to be colocalized with somatostatin. These results indicate that a significant part of the cholinergic influence upon hippocampal nonpyramidal neurons is relayed via SOMergic neurons.

Neurochemical anatomy of fetal hippocampus transplanted into large lesion cavities made in the adult rat brain

The purpose of the present study was to determine whether neurochemicals normally found within neuron somata, fibers, and terminals of the hippocampal formation would also be present in transplanted hippocampal tissue that had developed in lesion cavities made in adult rat brains by aspiration of the hippocampus and overlying dorsolateral neocortex. Embryonic Day 15 or 16 rat brian tissue containing hippocampus with some medial pallial anlage was transplanted into the site of hippocampal aspiration lesions in adult male rats. One hundred ten to one hundred thirty-five days later the brains of these rats were sectioned and processed using the avidin-biotin-horseradish peroxidase immunocytochemical procedure to visualize choline acetyltransferase, met-enkephalin (MENK), neurotensin (NT), somatostatin, substance P, tyrosine hydroxylase (TH), or vasoactive intestinal polypeptide. Sections from two brains were stained using the thiocholine technique for visualization of acetylcholinesterase. All of these substances were found within cell bodies and/or fibers in the transplants. However, several abnormalities were noted. In addition to TH-immunoreactive fibers, TH-immunoreactive cell bodies were found in the transplants. Since TH is not expressed in mature hippocampal or cortical neurons this suggests that mechanisms for suppression of manufacture of this enzyme are lacking or inhibited in the transplants. Further, although all of the peptides were present either in fibers or in both cell bodies and fibers, the density of staining for NT and MENK was less than would be expected for normal hippocampus, and none of the cell bodies or fibers reacting for the peptides exhibited any apparent organization resembling that normally observed in hippocampus or cortex. However, some histological organization was present and the cholinergic markers were associated with this organization. These data suggest that some tropic and/or trophic factor such as nerve growth factor is present in the transplants to guide cholinergic innervation.

Evidence that somatostatin enhances endogenous acetylcholine release in the rat hippocampus

The present experiments show that somatostatin (SS)-like immunoreactive material is present in the hippocampus and that its release can be increased by K+ stimulation of rat hippocampal slices, suggesting that SS-like peptides may be of significance to neurotransmission in the hippocampus. Exogenous SS-28 and SS-14 enhanced the K(+)-evoked release of endogenous acetylcholine (ACh) from rat hippocampal slices, whereas amino-terminal fragments of SS-28 did not. The increased ACh release in the presence of either peptide appeared to be mediated by an interaction with SS receptors because cyclo-SS, a putative SS antagonist, abolished the effects of both SS-28 and SS-14. In addition, the increase in ACh release induced by SS-14 or SS-28 was antagonized by the calcium channel antagonists omega-conotoxin GVIA, nifedipine, and cinnarizine, implicating voltage-sensitive calcium channels in this effect. Moreover, the effect was sensitive to tetrodotoxin, suggesting an indirect action of the peptides at a site distal to cholinergic nerve terminals. Cysteamine, which has been reported to deplete SS content and to increase SS release in brain, augmented the basal and evoked release of ACh from hippocampal slices, without affecting SS-like content and release. Finally, neuropeptide Y, which is colocalized with SS in many neurons of the hippocampal formation, did not alter ACh release, nor did it facilitate the SS-induced increase. The results suggest that in the rat hippocampus, both SS-28 and SS-14 interact with SS receptors to regulate ACh release indirectly by a mechanism that involves alterations of calcium influx during depolarization.

Somatostatin28(15-28), but not somatostatin28(1-12), affects central monoaminergic neurotransmission in rats

The effects of intracerebroventricularly (icv) administered somatostatin28(SS28) fragments, SS28(1-12) and SS28(15-28), were investigated on central monoaminergic neurotransmission in rats. SS28(15-28) did not significantly influence the hypothalamic and striatal noradrenaline concentrations. In a dose-related manner, SS28(15-28) significantly increased the dopamine, dihydroxyphenyl acetic acid DOPAC), and serotonin concentrations in hypothalamus, but did not modify these measures in striatum. The other SS28 metabolite, SS28(1-12), had no statistically significant effects on the monoamine neurotransmission. SS28(15-28) (6 and 9 nmol) induced barrel rotation, while SS28(1-12) was ineffective following administration over a wide dose-range (3-18 nmol). In conclusion, SS28(15-28) influences the hypothalamic monoaminergic transmission and causes barrel rotation, whereas SS28(1-12) has no neurochemical or behavioural effects in these tests.

Afferent and efferent synaptic connections of somatostatin-immunoreactive neurons in the rat fascia dentata

The aim of this study was to determine whether somatostatin (SS)-immunoreactive neurons of the rat fascia dentata are involved in specific excitatory circuitries that may result in their selective damage in models of epilepsy. Synaptic connections of SS-immunoreactive neurons were determined at the electron microscopic level by using normal and colchicine pretreated rats. Vibratome sections prepared from both fascia dentata of control animals and from rats that had received an ipsilateral lesion of the entorhinal cortex 30-36 hours before sacrifice were immunostained for SS by using a monoclonal antibody (SS8). Correlated light and electron microscopic analysis demonstrated that many SS-immunoreactive neurons in the hilus send dendritic processes into the outer molecular layer of the fascia dentata, and dendrites of the same neurons occupy broad areas in the dentate hilar area. The majority of SS-immunoreactive axon terminals form symmetric synapses with the granule cell dendrites in the outer molecular layer and also innervate deep hilar neurons. Via their dendrites in the outer molecular layer, the SS-immunoreactive neurons receive synaptic inputs from perforant pathway axons which were identified by their anterograde degeneration following entorhinal lesions. The axons from the entorhinal cortex are the first segment of the main hippocampal excitatory loop. The hilar dendrites of the same SS-immunoreactive cells establish synapses with the mossy axon collaterals which represent the second member in this excitatory neuronal chain. These observations suggest that SS-immunoreactive neurons in the dentate hilar area may be driven directly by their perforant path synapses and via the granule cells which are known to receive a dense innervation from the entorhinal cortex. These observations demonstrate that SS-immunoreactive neurons in the hilar region are integrated in the main excitatory impulse flow of the hippocampal formation.

Somatostatin immunohistochemistry of hippocampal slices with lucifer yellow-stained pyramidal neurons responding to somatostatin

We have combined electrophysiology and immunohistochemistry to study the somatostatin (SS) innervation of neurons in the rat hippocampal slice. After recording the intracellular response of a pyramidal CA1 neuron in vitro to SS, Lucifer Yellow was injected into the cell and the slice fixed and processed for immunohistochemical localization of SS in the vicinity of the recorded neuron. Most pyramidal neurons (70%) responded to SS with a hyperpolarization associated with marked slowing of spontaneous discharge and reduced input resistance. SS-containing elements either crossed, ran parallel or seemingly terminated on the Lucifer Yellow-filled SS-responsive cell. These occurrences of close proximity of apparent pre- and postsynaptic elements were observed in all layers of the CA1 region and may represent synaptic terminations of SS elements on a pyramidal neuron that are likely to elicit membrane hyperpolarizations.

Behavioral correlates of theta-on and theta-off cells recorded from hippocampal formation of mature young and aged rats

Most hippocampal formation single units in freely behaving rats fall into one of two categories (Ranck 1973). The most obvious behavioral correlate of complex-spike (CS) cells is spatially selective discharge (O'Keefe and Dostrovsky 1971), while theta cells show increased firing in phase with the EEG theta rhythm associated with Vanderwolf's Type I behaviors (e.g. walking, exploration). Recently, Colom and Bland (1987) described, in urethane anesthetized animals, a class of non-CS cell which was inactive in the presence of EEG theta and discharged continuously during LIA. They called these "theta-off" cells and used the term "theta-on" to refer to the classical "theta" cell. We describe the behavioral correlates of 14 theta-off cells encountered in CA1 (n = 1), hilus fascia dentata (FD; n = 4), subiculum (n = 6), abd entorhinal cortex (n = 3). These cells were encountered very infrequently in the course of several experimental investigations of mature young and old rats involving 885 hippocampal neurons recorded from 33 rats during radial maze performance. Fourteen theta-on cells encountered within a few hundred microns of the sites where theta-off cells were recorded were included for comparison. Both theta-on and theta-off cells discharged single spikes and did not show CS bursting characteristic of pyramidal cells. Theta-off cells, however, exhibited significantly greater spike durations than theta-on cells. Mean rates for theta-on and theta-off cells were 8.7 Hz and 6.5 Hz, respectively. Maximum rates were 114 Hz and 104 Hz, respectively. Some cells of both types showed 6-8 Hz modulation while animals traversed the maze.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of somatostatin mRNA in the rat nervous system as visualized by a novel non-radioactive in situ hybridization histochemistry procedure

The cellular localization of preprosomatostatin mRNA in the rat brain and sensory ganglia has been examined in detail using a newly developed highly sensitive non-radioactive in situ hybridization histochemistry procedure. An alkaline phosphatase labelled anti-sense 30mer oligodeoxynucleotide probe was used for detection of somatostatin mRNA. This probe readily demonstrated somatostatin gene expression throughout the rat CNS with very high contrast and good cellular localization. As a result, we visualized numerous somatostatin mRNA-positive cells in many CNS areas which had previously not been shown to contain a mRNA signal. This method detected a number of somatostatin mRNA-positive cells, in the mitral cell layer of accessory olfactory bulb, the glomerular layer of the main olfactory bulb, the dorsal part of the lateral septum, superficial gray layer of superior colliculus, inferior colliculus, anterior ventral cochlear nucleus, granular layer and Purkinje cell layer of cerebellum, and substantia gelatinosa of medulla and spinal cord, all areas where signal detection using radiolabelled in situ probes has previously been rather difficult. The principle advantages of the present method include the very precise cellular resolution of signal, the rapid reaction time and low background. The sensitivity of the present method seems to be at least equivalent to most immunocytochemical procedures and more sensitive than most isotopic in situ hybridization methods.

Similarities in circuitry between Ammon's horn and dentate gyrus: local interactions and parallel processing

We present a "model" of hippocampal information processing based on a review of recent data regarding the local circuitry of Ammon's horn and the dentate gyrus. We have been struck by the parallels in cell type and connectivity in Ammon's horn and the dentate gyrus, and have focused on similarities between CA3 pyramidal cells and mossy cells. Important conclusions of our analysis include the following: (1) The idea of serial processing of afferent information, from one hippocampal subregion to the next, is inadequate and based on an over-simplification of circuitry; information processing undoubtedly occurs over parallel, as well as serial, pathways. (2) Local circuitry within a given hippocampal subregion gives rise predominantly to feedforward inhibition; recurrent inhibition is present, but less potent. (3) There are multiple populations of local circuit neurons, each of which has a specific function, characteristic interconnections, and special cell properties. It is misleading to categorize these cells into a single category of inhibitory interneuron.

Quantitative radioautographic study of somatostatin receptors heterogeneity in the rat extrahypothalamic brain

The possible heterogeneity of extrahypothalamic somatostatin receptors was studied in rat brain by quantitative radioautography. The respective distribution and relative proportion of two somatostatin receptor sub-types (SS1 and SS2) were assessed by using two radioligands, the non-selective probe [125I]Tyr3-D-Trp8-somatostatin14 and the SS1 selective analogue [125I]Tyr3-SMS 201-995. For both ligands, adjacent brain sections were processed in the presence of micromolar concentrations of either a non-discriminative competitor (somatostatin14) or SS1-selective analogue (SMS 201-995). The comparative analysis of the specific binding remaining in the presence of each non-radioactive competitor permitted a semi-quantitative analysis of the proportion of SS1 and SS2 receptor sub-types in each brain region examined. Data obtained correlate well with homogenate binding results reported previously [Reubi J. C. (1984) Neurosci. Lett. 49, 259-263]. Although the distribution patterns obtained with both radioligands were similar, [125I]Tyr3-SMS 201-995 labelled only a fraction of [125I]Tyr0-D-Trp8-somatostatin14-labelled sites in certain brain regions. For example, both superficial and deep cortical laminae, as well as the basolateral amygdaloid nucleus and CA1 hippocampal area exhibited different binding densities with [125I]Tyr0-D-Trp8-somatostatin14 depending on the competitor used in the assay (somatostatin14 or SMS 201-995). On the other hand, [125I]Tyr3-SMS 201-995 binding was eliminated in an identical fashion by either competitor in these very same brain areas. This suggests the existence of SS1 and SS2 somatostatin receptor sub-types in these regions. In all other brain areas examined, somatostatin receptor sites are apparently of the SS1 sub-type. The heterogeneity of somatostatin receptors observed in certain regions may have relevance for the various biological effects induced by somatostatin in the central nervous system.

Calbindin D-28k and parvalbumin in the rat nervous system

This paper describes the distribution of structures stained with mono- and polyclonal antibodies to the calcium-binding proteins calbindin D-28k and parvalbumin in the nervous system of adult rats. As a general characterization it can be stated that calbindin antibodies mainly label cells with thin, unmyelinated axons projecting in a diffuse manner. On the other hand, parvalbumin mostly occurs in cells with thick, myelinated axons and restricted, focused projection fields. The distinctive staining with antibodies against these two proteins can be observed throughout the nervous system. Calbindin D-28k is primarily associated with long-axon neurons (Golgi type I cells) exemplified by thalamic projection neurons, strionigral neurons, nucleus basalis Meynert neurons, cerebellar Purkinje cells, large spinal-, retinal-, cochlear- and vestibular ganglion cells. Calbindin D-28k occurs in all major pathways of the limbic system with the exception of the fornix. Calbindin D-28k is, however, also found in some short-axon cells (Golgi type II), represented by spinal cord interneurons in layer II and interneurons of the cerebral cortex. It is also detectable in some ependymal cells and abundantly occurs in vegetative centres of the hypothalamus. The "paracrine core" of the nervous system and its adjunct (1985, Nieuwenhuys, Chemoarchitecture of the Brain. Springer, Berlin) is very rich in calbindin D-28k. The distribution of calbindin D-28k-positive neurons is very similar to that of the dihydroperydine subtype of calcium channels. Most of the cells containing calbindin D-28k are vulnerable to neurodegenerative processes. Parvalbumin-immunoreactive neurons have a different, and mostly complementary distribution compared with those which react with calbindin D-28k antisera, but in a few cases (Purkinje cells of the cerebellum, spinal ganglion neurons), both calcium-binding proteins co-exist in the same neuron. Many parvalbumin-immunoreactive cells in the central nervous system are interneurons (Golgi type II) and, to a lesser extent, long-axon cells (Golgi type I), whereas conditions are vice versa in the peripheral nervous system. Intrinsic parvalbuminic neurons are prominent in the cerebral cortex, hippocampus, cerebellar cortex and spinal cord. Long-axon parvalbumin-immunoreactive neurons are, for example, the Purkinje cells, neurons of the thalamic reticular nucleus, globus pallidus, substantia nigra (pars reticulata) and a subpopulation among large spinal-, retinal-, cochlear- and vestibular ganglion cells. Parvalbumin is rich in cranial nerve nuclei related to eye movements. In addition to nervous elements, parvalbumin immunoreactivity occurs in a few ependymal cells and in some pillar cells of the organ of Corti.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of somatostatin-28 and some of its fragments and analogs on open-field behavior, barrel rotation, and shuttle box learning in rats

The effect of intracerebroventricular (ICV) administration of somatostatin-28 (SS-28) and some of its fragments, SS-28 (1-12), SS-28(15-28), and analogs, des-AA-(1,2,4,5,12,13)-(DTrp8)SS-14, ODT8-SS, and (DTrp8,DCys14)SS-14 were studied in different behavioral tests on rats. SS-28 (6.0 nM) decreased, SS-28(15-28) (0.6 nM) increased, and SS-28(15-28) (6.0 nM) decreased activity of the animals in an open-field test. SS-28(1-12) (0.6, 3.0, and 6.0 nM) did not influence this behavior. ODT8-SS (0.6, 3.0, and 6.0 nM) decreased activity of the rats, while (DTrp8,DCys14)SS-14 increased it, only at a high dose (6.0 nM). Similar results were obtained for barrel rotation, except that (DTrp8,DCys14)SS-14 even in high dose (12.0 nM) had no effect. In a shuttle-box learning paradigm, SS-28(15-28) (0.6 nM) facilitated, while SS-28(1-12) (0.6 nM) did not influence, the performance of the animals. These results suggest that the isomeric Cys(28) form of the SS-28(15-28) molecule may be crucial for the expression of the behavioral effects of these peptides.

Ultrastructural localization of somatostatin-like immunoreactivity in the rat dentate gyrus

Neurons containing somatostatin (SOM) are enriched in the dentate gyrus. We sought to establish the ultrastructural localization of this peptide in the dentate gyrus of the rat brain with a double-bridged peroxidase-antiperoxidase (PAP) method localizing antisera directed against somatostatin (SOM)-28 and SOM-28. Initial light microscopic observations confirmed that the majority of perikarya and thick varicose processes with intense SOM-like immunoreactivity (SOM-LI) were observed in the hilus. Fine varicose processes with SOM-LI were found throughout all layers of the dentate gyrus but were most intense in the outer third of the molecular layer (ML), where an occasional perikaryon with SOM-LI was seen. By electron microscopy, SOM-LI was found in neuronal perikarya, dendrites, axons, and axon terminals. Two types of SOM-containing perikarya were observed. The first type was small (6-10 microns), round or avoid, and had a labeled cytoplasma with abundant Golgi complexes and a dense accumulation of PAP-reaction product. The second type of perikarya was larger (11-16 microns) and had a more abundant cytoplasm than the first type, but the Golgi complexes did not appear labeled. Most (96% of 374) of the synapses on the SOM-labeled perikarya and dendrites were from terminals without SOM-LI which formed nearly equal proportions of asymmetric and symmetric junctions. The remainder of the presynaptic terminals contained SOM-LI and made primarily symmetric synapses. Synaptic junctions from both unlabeled and labeled terminals were primarily on the shafts of the small (0.5-1.5 microns) SOM-immunoreactive dendrites. The terminals with SOM-LI (0.25-1.3 microns) contained many small, clear vesicles and from zero to four large dense-core vesicles. Terminals with SOM-LI were associated 1) with one unlabeled perikaryon or dendrite (49% of 215 in the hilus; 76% of 326 in the ML); 2) with two unlabeled perikarya or dendrites simultaneously (5% hilus; 4% ML); and 3) with one SOM-containing perikaryon or dendrite (6% hilus; 3% ML). In all three types of associations, synaptic contacts on perikarya were few while the majority were with small (distal) dendrites. Moreover, most of the terminals with SOM-LI formed symmetric junctions or lacked membrane specializations but were without any apparent glial intervention in the plane of section analyzed. The remaining SOM-labeled terminals (40% hilus; 17% ML) were without any apparent synaptic relations. However, a few of these terminals were in direct apposition to other terminals, some of which were also SOM-immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)

The postnatal expression of acetylcholinesterase in somatostatin-positive cells of mouse hippocampus

The neuroanatomical distributions of acetylcholinesterase (AChE) staining and somatostatin-like immunoreactivity (SOMLI) of neurons intrinsic to the mouse hippocampal formation have been evaluated during postnatal development. Besides the progressive development of neuropil staining for AChE, as a consequence of the septohippocampal innervation, intense AChE staining was also expressed in a subpopulation of neurons intrinsic to the stratum oriens and the hilus of dentate gyrus. In the stratum oriens, the number of AChE-positive cells increased between postnatal day (PND) 3 and PND 10 and declined slightly after PND 21. In the hilus of the dentate gyrus, the number of AChE-stained cell bodies increased progressively until PND 21 when the adult complement was achieved. The AChE-positive neurons of strata radiatum and lacunosum-moleculare, which were few and scattered, increased progressively from PND 7 until adulthood. SOMLI-positive neurons were present in the hippocampal formation by PND 3, and their density showed initial increases followed by decreases in the second to third postnatal week. SOMLI cell distribution on the other hand did not change remarkably during subsequent maturation. Because of the similar developmental time course and localization of AChE and SOMLI neurons, co-localization was assessed by a double-staining method. A large percentage of the neurons staining for one of these markers also stained for the other. In the stratum oriens, from PND 3 to PND 10, the number of SOMLI neurons expressing AChE was increased while a slight decrease from the PND 21 to adulthood was evident. Virtually all SOMLI-positive neurons in the dentate gyrus stained for AChE from PND 7 through adulthood, although the intensity of AChE reactivity declined with maturation.

Distribution of somatostatin-like immunoreactivity in the monkey amygdala

The distribution of somatostatin-like immunoreactivity was studied in the macaque monkey (Macaca fascicularis) by using primary antisera that recognize somatostatin-28 (S309) or somatostatin-28(1-12) (S320). Somatostatin-immunoreactive neuronal cell bodies were observed in all amygdaloid nuclei and cortical regions. The density of labeled cells varied substantially, however, both within and across the various amygdaloid subdivisions. The highest densities of labeled neurons were observed in layer III of the periamygdaloid cortex, in layers II and III of the medial nucleus, in the magnocellular division of the accessory basal nucleus, and in the medial portion of the lateral nucleus. Many labeled cells were also consistently observed in the caudoventral portion of the lateral division of the central nucleus. Labeled cells were heterogeneous in size and shape ranging from small and spherical to large and multipolar. The density of somatostatin-immunoreactive fibers also varied greatly from region to region and was often inversely related to the density of immunoreactive cells. Highest densities of immunoreactive fibers were observed in the periamygdaloid cortex, medial nucleus, parvicellular division of the accessory basal nucleus, paralaminar nucleus, ventrolateral portion of the lateral nucleus, parvicellular division of the basal nucleus, and the lateral division of the central nucleus. Fibers and terminals in the central nucleus had a coarsely varicose appearance and this pattern of staining was continuous along the trajectory of the central nucleus projection to the bed nucleus of the stria terminalis. The large, immunoreactive varicosities located in this area often appeared to outline dendritic or vascular profiles within the substantia innominata. The lowest levels of somatostatin-immunoreactive fibers were observed in the magnocellular division of the basal nucleus and in the ventromedial portion of the accessory basal nucleus.

Ultrastructural analysis of somatostatin-immunoreactive neurons and synapses in the temporal and occipital cortex of the macaque monkey

Somatostatin-containing neurons and terminals have been analyzed in monkey temporal and occipital cortex by using light and electron microscopic immunohistochemistry. An antibody against Somatostatin-28, that was shown previously preferentially to label fibers (Morrison et al.: Brain Research 262:344-351, 1983), was utilized. As expected, few cell bodies were labeled. At the electron microscopic level, labeled cells presented a characteristic asymmetric position of the nucleus and very few symmetric or asymmetric synapses on the somatic surface. In all areas examined, somatostatin fibers formed a dense plexus in the most superficial layers (I-upper III). The density of labeled fibers in intermediate (deep III-IV) and deep layers (V-VI) varied considerably among areas. The synaptic relationships of the immunoreactive fibers were analyzed and postsynaptic targets quantified in V1, V2, and the superior and inferior temporal gyrus (STG and ITG, respectively). The synapses formed by somatostatin-labeled boutons were of the symmetric type (type II) and the primary postsynaptic targets were dendritic shafts. No regional differences were found in the distribution of the postsynaptic targets in layers I-upper III. The pattern of synapses in the deep layers was examined in STG. The frequency and distribution of postsynaptic targets was similar to the superficial layers of STG and the other temporal and occipital regions. In intermediate layers of the temporal cortex areas there was an increase in the proportion of synapses on dendritic spines. In a correlated light and electron microscopic analysis we examined synapses made by radial fibers in these regions and found that although the main targets are distal dendritic shafts, almost 40% of synapses were on dendritic spines. We suggest that the radial fibers may originate from a specialized interneuron, previously described as the double bouquet cell, and that this particular subset of somatostatin-containing double bouquet cells is likely to exhibit a very high degree of regional heterogeneity with a preference for association cortices with extensive corticocortical convergence.

Development of somatostatin-like immunoreactivity in the hippocampal formation of normal and reeler mice

Using antisera directed against somatostatin-28 or somatostatin-28(1-12), the development of somatostatin-like immunoreactivity (SS-LI) was examined in the hippocampal formation of normal and reeler mice. As early as postnatal day 5, SS-labeled neurons exhibit the adult pattern of distribution in the normal hippocampal formation, these neurons being situated predominantly in the stratum oriens of the hippocampus and the hilus of the dentate gyrus. In contrast, SS-labeled neurons in the reeler hippocampal formation are dispersed throughout the various layers, reflecting the disrupted laminar organization of the hippocampus in this mutant. In both the normal and reeler hippocampal formation, SS-labeled fibers are most abundant in the stratum lacunosum moleculare. However, in the reeler, there appears to be increase in the density of SS-LI fibers, not only in the stratum lacunosum moleculare but also in the stratum oriens, stratum radiatum and pyramidal cell layer of the hippocampus.

VIP-, SS-, and GABA-like immunoreactivity in the mid-hippocampal region of El (epileptic) and C57BL/6 mice

The El (epileptic) mouse is a model of hereditary sensory precipitated temporal lobe epilepsy. We compared vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI), somatostatin-like immunoreactivity (SS-LI), and gamma-aminobutyric acid-like immunoreactivity (GABA-LI) in the mid-hippocampal region of El and C57BL/6 mice. Specific interneuron populations with VIP-LI and GABA-LI were elevated in the El mice, whereas SS-LI populations were unchanged. These neurochemical alterations may be contributing to the epileptic predisposition of El mice.

Further studies of the effects of somatostatin and related peptides in area CA1 of rabbit hippocampus

1. In slice studies of mature and immature CA1 hippocampal pyramidal cells from rabbit, somatostatin 14 (SS14), the related peptide somatostatin 28(1-12) [SS(1-12)], and the synthetic analogue of somatostatin 14, SMS-201995 (SMS), had similar effects. When pressure-ejected onto cell somata, these peptides elicited depolarizations, often accompanied by action potential discharge. When applied to dendrites, the peptides produced depolarizations or hyperpolarizations. 2. When a large amount of one of the three somatostatin-related (SS) peptides was applied to the slice at some distance from the impaled cell, hyperpolarizations were observed that were not always blocked by tetrodotoxin (TTX) or low Ca2+. Since SS peptides were also found to depolarize interneurons in area CA1, it seems likely that the hyperpolarizations that were blocked by TTX or low Ca2+ were mediated via excitation of interneurons that in turn hyperpolarized pyramidal cells. 3. All SS peptides also had long-lasting effects on CA1 pyramidal cells that led to spontaneous firing of action potentials and an increase in the number of action potentials discharged in response to a given depolarizing current pulse; the spontaneous discharge effect was blocked by TTX or low Ca2+ plus Mn2+ and, thus, appeared to have a presynaptic mechanism. However, the increase in discharge in response to a constant depolarizing current pulse was not dependent on intact synaptic transmission and, therefore, was attributable to a direct postsynaptic effect of the SS peptides.

Neuronal localization of prosomatostatin mRNA in the rat brain with in situ hybridization histochemistry

Individual neurons containing prosomatostatin mRNA were identified with in situ hybridization histochemistry. Our results demonstrate a widespread distribution of prosomatostatin mRNA in several regions of the rat central nervous system. Neurons containing this transcript were most abundant in the anterior olfactory nucleus, hypothalamus, hippocampus, and amygdala as well as in all regions of the cerebral cortex. Moreover, the distribution of mRNA-containing perikarya was coextensive with the location of neurons containing somatostatin-like immunoreactivity in all areas of the brain examined. Somatostatin neurons varied in their morphology and amount of hybridization signal from region to region. The widespread distribution and regional variations in neuronal morphology and the amount of hybridization signal are consistent with a neurotransmitter and/or a neuromodulator role for somatostatin in addition to its well-established neuroendocrine role. These results demonstrate that both the peptide and its mRNA are found in perikarya in the same areas and that they are therefore the sites of synthesis for somatostatin.

Viral infection of neurons can depress neurotransmitter mRNA levels without histologic injury

Neonatal mice inoculated with lymphocytic choriomeningitis virus (LCMV) have non-lytic persistent neuronal infection and disturbed behavior. We now show that LCMV replicates in neurons containing the neurotransmitter somatostatin without morphologic evidence of injury and that persistent neuronal LCMV infection in mice is attended by a decrease in brain levels of somatostatin mRNA. Brain levels of mRNA for another neurotransmitter peptide, cholecystokinin, are not decreased. These data are the first to localize a virus to a specific neurotransmitter-containing cell during in vivo infection and suggest that persistent viral infections could cause neurologic or psychiatric diseases through selective effects on brain levels of neurotransmitter mRNAs.

The time of origin of somatostatin-immunoreactive neurons in the rat hippocampal formation

Experiments utilizing a combination of [3H]thymidine autoradiography and immunohistochemistry were conducted to determine the time of origin of somatostatin-immunoreactive (SSIR) neurons in the hippocampal formation of the rat. A quantitative and topographic description of neurogenesis in this peptide-containing neuronal system was generated using a computer-aided system to plot the position of labeled cells. Dissected and 'flattened' hippocampal preparations were used to facilitate the analysis of spatial gradients of SSIR cell development. The results indicate that most SSIR hippocampal cells are generated during a short embryonic period which extends from the 12th through the 15th day of gestation (E12-E15). Within this period of development, the distribution of SSIR cells follows a spatial gradient along the transverse or subiculo-dentate axis of the hippocampus. The earliest formed SSIR neurons, generated on E12 and E13, are preferentially distributed to the subiculum, those generated on E14 are most commonly observed throughout the CA1-CA3 fields of the hippocampus and SSIR neurons which become postmitotic on E15 are more heavily represented in the hilar region of the dentate gyrus than cells born at other stages of development. There was no clear-cut neurogenic gradient along the septotemporal axis of the hippocampus. These results indicate that somatostatin cells in the rat hippocampal formation are generated during the same prenatal period when glutamic acid decarboxylase (GAD)-positive neurons become postmitotic. These studies also suggest that quantitative developmental analyses of chemically specific cell types can reveal prominent features of cortical ontogeny that are not readily apparent in standard [3H]thymidine preparations.

Somatostatin(14) and -(28) but not somatostatin(1-12) hyperpolarize CA1 pyramidal neurons in vitro

The three major prosomatostatin-derived peptides found within CNS neurons are a 28-amino acid peptide (SS28), a cyclic 14 amino acid peptide (SS14) and a 12 amino acid peptide (SS1-12). Immunohistochemical studies demonstrate a differential distribution of these related forms of somatostatin within CNS neurons and have led to the suggestion that SS1-12 may represent the predominant neurotransmitter form of this family of peptides. Intracellular recordings from CA1 pyramidal neurons in the in vitro rat hippocampal slice revealed that application of SS14 and SS28 in nanomolar concentration produced neuronal hyperpolarization; synaptic responses, recorded extracellularly, were also reduced. In contrast, we were unable to demonstrate a pre- or postsynaptic action of SS1-12 on these neurons. These results do not support the hypothesis that SS1-12 functions as a central neurotransmitter in area CA1 of the hippocampus.

Development of somatostatin-containing neurons and fibers in the rat hippocampus

Using a combination of in situ hybridization and immunohistochemistry, the development of somatostatin (SS)-containing neurons and fibers was examined in the rat dorsal hippocampus and dentate gyrus. The major development of this hippocampal peptidergic system occurs postnatally. At postnatal day 1 (P1), neurons containing SS mRNA are evident primarily in the stratum oriens, but also in the hilus of the dentate gyrus. Similar neurons are also immunoreactive for SS28 and SS28(1-12), suggesting a minimal lag in the transcription of SS mRNA and its translation into specific SS peptides. The number of SS neurons increases postnatally to P10, followed by a decrease in number in the adult. This transient change in the number of SS neurons coincides with dramatic changes in SS28(1-12)-immunoreactive fibers, which are initially present in the stratum lacunosum moleculare, with no significant immunoreactivity in the dentate gyrus. By P15, the molecular layer of the dentate gyrus is densely innervated, while similar immunoreactivity in the stratum lacunosum moleculare is greatly reduced. These data are consistent with a transient projection from the stratum oriens to the stratum lacunosum moleculare, which is replaced by a projection from the hilus to the molecular layer of the dentate gyrus as this structure matures.

Immunocytochemical localization of somatostatin in the cerebral cortex of lizards

The distribution of somatostatin-like immunoreactivity in the cerebral cortex of two lizards has been studied. Results are similar in both species. Somatostatin-positive neurons show variable morphology; they are bipolar, multipolar or pyramidal cells. Their distribution within the cerebral cortex is not homogeneous: they tend to be found in the innermost cortical layer, the deep plexiform layer, where they constitute a constant population in the region of the dorsomedial cortex. All immunoreactive processes observed in the cerebral cortex belong to somatostatin cortical neurons since no immunoreactive fiber is found to reach or leave the telencephalic cortex. Most of the dendrites are smooth or sparsely spinous. Axons are abundant in the deep plexiform layer; in the dorsomedial cortex a prominent terminal field appears in the outermost region of the superficial plexiform layer, which may arise from the neuronal somatostatin immunoreactive population found deeper in the same cortex.

Topographical relationship between the entorhinal cortex and the septotemporal axis of the dentate gyrus in rats: II. Cells projecting from lateral entorhinal subdivisions

Projections from the rat lateral entorhinal cortex (area 28-l) to the dentate gyrus were traced and then interpreted according to a parcellation scheme that recognized four cytoarchitectonic subdivisions of area 28-l: areas dorsolateral (dl), ventrolateral (vl), ventromedial (vm), and TR. Following lesions of area 28-l, anterograde degeneration was traced with the Fink-Heimer method. In parallel experiments iontophoretic injections of horseradish peroxidase (HRP) were made in the lateral perforant path terminal zone of the dentate molecular layer. Retrograde neuronal labeling patterns within area 28-l were charted following dorsal, midseptotemporal (mid ST), and ventral dentate injections. In two additional cases HRP was deposited in the ventral subiculum. Lesions of area dl (which lies entirely on the posterolateral cortex) produced terminal degeneration that was confined to the dorsal one-half of the dentate gyrus. Lesions involving primarily areas vl and vm (which lie on the posteroinferior cortex) caused a complementary pattern of degeneration; silver grains predominated in the ventral dentate gyrus. Injections of HRP into the outer dentate molecular layer labeled layer II neurons within area 28-l. Deposits of HRP in the dorsal one-third of the dentate gyrus labeled a rostrocaudal strip of neurons within the dorsal one-third of area dl; no other subdivisions of area 28-l contained labeling. After mid-ST deposits of HRP, a rostrocaudally oriented strip of labeled cells appeared in the ventral one-third of area dl. Mid-ST injections also labeled neurons in the caudolateral quadrant of area vl. Injection of HRP into the ventral dentate gyrus labeled neurons in the caudomedial quadrant of area vl as well as a few neurons in caudal area vm. No labeled cells were ever found in area dl following ventral dentate HRP deposits. Neurons within area TR were never retrogradely labeled from injections of HRP into the dentate perforant path zone. However, ventral subicular injections of HRP labeled a few cells in the posterior part of area TR, as well as hundreds of neurons throughout the rostrocaudal extent of area vl. The results indicate a highly organized innervation of the dentate gyrus by several subdivisions of area 28-l. In area dl, rostrocaudal strips of layer II neurons innervate distinct segments of the dorsal ST axis. The posterior half of areas vl and vm innervates the ventral half of the ST axis; a lateromedial gradient there corresponds to increasingly ventral terminations along the dentate ST axis.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin depresses excitability in neurons of the solitary tract complex through hyperpolarization and augmentation of IM, a non-inactivating voltage-dependent outward current blocked by muscarinic agonists

The synaptic function of somatostatin-containing fibers in the nervous system is controversial. Therefore, we used a slice preparation of the rat brain stem to test the electrophysiological effects of prosomatostatin-derived peptides on neurons of the solitary tract complex, which contains an abundance of somatostatin-containing fibers and cell bodies. Superfusion of both somatostatin-14 and somatostatin-28 (the precursor for somatostatin-14), but not somatostatin-28-(1-12) or -(1-10), predominantly inhibited spontaneous spike and subthreshold (probably synaptic) activity. In intracellular recordings, somatostatin-14 and -28 hyperpolarized most neurons in association with a slight (10-35%) but reproducible decrease in input resistance. These hyperpolarizing responses were augmented in depolarized cells and persisted in cells in which spontaneous inhibitory postsynaptic potentials became depolarizing after Cl- injection. These data suggest that somatostatin receptors regulate a K+ conductance. In voltage-clamp studies, somatostatin-28 and -14 induced a steady outward current and augmented the voltage-dependent, nonactivating outward K+ conductance (IM) shown to be blocked by activation of muscarinic cholinergic receptors. These results suggest (i) that somatostatin-containing elements in the solitary tract complex play an inhibitory role through the activation of postsynaptic permeability to potassium ions and (ii) that the same ion channel type may be coregulated by two neurotransmitter candidates, somatostatin and acetylcholine, through a reciprocal control mechanism.

Somatostatin augments the M-current in hippocampal neurons

Immunocytochemical and electrophysiological evidence suggests that somatostatin may be a transmitter in the hippocampus. To characterize the ionic mechanisms underlying somatostatin effects, voltage-clamp and current-clamp studies on single CA1 pyramidal neurons in the hippocampal slice preparation were performed. Both somatostatin-28 and somatostatin-14 elicited a steady outward current and selectively augmented the noninactivating, voltage-dependent outward potassium current known as the M-current. Since the muscarinic cholinergic agonists carbachol and muscarine antagonized this current, these results suggest a reciprocal regulation of the M-current by somatostatin and acetylcholine.

GABAergic neurons containing somatostatin-like immunoreactivity in the rat hippocampus and dentate gyrus

The distribution of somatostatin-like immunoreactive (SS-LI) material and its colocalization with glutamic acid decarboxylase (GAD)-like immunoreactivity were studied in the rat hippocampus and dentate gyrus neurons using immunohistochemistry. In the dentate gyrus and CA1 region, SS-LI perikarya were concentrated in the hilus and in the stratum oriens, respectively, whereas immunoreactive cell bodies were rarely seen in other layers. Approximately half of the SS-LI neurons of the CA3 region were situated in the stratum oriens, the other half being scattered in strata pyramidale, lucidum and radiatum. About 90% of SS-LI neurons were also GAD-like immunoreactive, whereas about 14% of GAD-like immunoreactive (GAD-LI) neurons were SS-like immunoreactive. The percentage of GAD-LI neurons which were also immunoreactive for SS varied from one layer to the other. This percentage was about 30% in the hilus of the dentate gyrus and in the stratum oriens of the CA1 and CA3 regions; it was 5-10% in the strata pyramidale, lucidum and radiatum of the CA3 region and reached only 2% in the granule cell layer and molecular layer of the dentate gyrus and in the stratum pyramidale and stratum radiatum in the CA1 region. These observations indicate that the majority of SS-LI neurons in the rat hippocampal formation are a subpopulation of GABAergic neurons.

Somatostatin in neuropsychiatric disorders

1. Somatostatin is a peptide that is widely and discretely distributed throughout the central nervous system. 2. Its relevance to neuropsychiatric disorders is suggested both by the existence of disease-related alterations in somatostatin content in brain and cerebrospinal fluid as well as by the manifold neuroregulatory capabilities of somatostatin and related peptides. 3. This article will summarize the central nervous system effects of somatostatin, identify those neuropsychiatric disorders that are characterized by changes in somatostatin, and review the evidence for and potential significance of decreases in cerebrospinal fluid somatostatin in depression.

Ultrastructural characterization and GAD co-localization of somatostatin-like immunoreactive neurons in CA1 of rabbit hippocampus

Immunocytochemical techniques have been used to identify a striking interneuronal population which is immunoreactive for the peptide, somatostatin. The cell population, which is seen most densely in stratum oriens and at the oriens/alveus border of the CA1 region of rabbit hippocampus, was characterized in light and electron microscopic observations. The cells have dendrites which extend parallel to and into the alveus, with occasional processes ascending through stratum pyramidale toward the hippocampal fissure. The dendrites receive numerous synaptic contacts directly onto aspinous dendritic shafts. Axon collaterals ramify profusely within the pyramidale region, and among the proximal apical and basal pyramidal cell dendrites in areas of stratum radiatum and stratum oriens. Somatostatin-like immunoreactive terminals make synaptic contact, primarily of the symmetric type, with the somata and proximal dendrites of pyramidal neurons. Somatostatin-like neurons are found at approximately equal density in the hippocampus of immature (8 days postnatal) and mature (30 days postnatal) rabbit. Double-labelling techniques, to identify both somatostatin-like and glutamic acid decarboxylase (GAD) immunoreactive neurons, demonstrated that a large proportion of the somatostatin neurons were also GABAergic.

The survival of dentate gyrus neurons in dissociated culture

Using a technique for dissociating cells from the area dentata of postnatal rats, we have been able to routinely establish low density cultures of dentate granule neurons that can be grown in the presence or absence of serum. Non-granule neurons from the hilar region and glial cells (both astrocytes and oligodendrocytes) are also present, but can be readily distinguished from the granule cells in these cultures. Unlike dissociated hippocampal pyramidal cells, which frequently resemble their in vivo morphology, dissociated dentate granule cells bear little resemblance to their normal in vivo counterparts, but are very similar in appearance to the ectopic granule cells seen in the reeler mouse. This suggests that extrinsic factors are the principal determinants of the mature form which granule neurons assume in vivo. On the other hand, the dissociated granule cells are able to express certain other aspects of their in vivo phenotype including the synthesis and transport of an antigen which is characteristically found in mossy fibers. Certain neuropeptide-containing non-granule neurons found in these cultures are also capable of maintaining aspects of their in vivo phenotype.

Comparison of substance K-like and substance P-like fibers and cells in the rat hippocampus

Substance P (SP) and substance K (SK) are structurally related peptides which are both encoded in the preprotachykinin A gene. The distribution of SP- and SK-like fibers and cell bodies in the rat hippocampus were studied by immunohistochemistry. The distribution of SK-like fibers was similar to that of SP-like fibers but there were few SK-like fibers. Fibers for both peptides were prominent in the dorsal and ventral subiculum and at the junction of CA2 and CA3. SP- and SK-like cell bodies were noted in the subiculum and in the stratum oriens of CA1 and CA2. SP- and SK-like cells were also noted in the ventral dentate gyrus but only SP-like cells were found in the dorsal dentate gyrus.

Ontogeny of somatostatin-like immunoreactivity in the human fetus and infant spinal cord

The localization and distribution of somatostatin like-immunoreactivity (SSLI) in postmortem human fetus and infant spinal cord and dorsal root ganglia were studied by using the indirect immunofluorescence technique. SSLI, which was mostly located within varicose fibers and terminal-like structures, occasionally within cell bodies, was detected during early fetal life (on gestational week 9 and beyond). The changes occurring from the early to the late fetal and infant stages mainly resulted in a progressive increase in the number of somatostatin-like immunoreactive fibers within most of the gray areas. On the whole the majority of immunolabelled fibers and terminal-like structures were observed over the superficial layers of the dorsal gray including the marginal zone and the substantia gelatinosa. Other regions displaying a moderate number of somatostatin-like immunoreactive fibers were the intermediate gray and the gray commissure area around the central canal. A few scattered immunofluorescent fibers were unevenly distributed over the white matter especially in the lateral and ventral funiculus areas and near the ventral motor nuclei. A few somatostatin-like immunoreactive cell bodies were occasionally found in the superficial layers of the dorsal gray and in the intermediolateral gray. Immunolabelled cells were further usually visualized in dorsal root ganglia. Although the distribution patterns of somatostatin-like immunoreactive structures were similar throughout the entire spinal cord, the highest density of immunolabeled fibers, however, was seen at the lumbosacral level. Our results indicate that in the human spinal cord SSLI is already widespread before birth. It is further suggested that somatostatin ontogenesis in human spinal cord and dorsal root ganglia begins early in fetal life.

GABAergic neurons containing the Ca2+-binding protein parvalbumin in the rat hippocampus and dentate gyrus

The distribution of Ca2+-binding protein, parvalbumin (PV), containing neurons and their colocalization with glutamic acid decarboxylase (GAD) were studied in the rat hippocampus and dentate gyrus using immunohistochemistry. PV immunoreactive (PV-I) perikarya were concentrated in the granule cell layer and hilus in the dentate gyrus and in the stratum pyramidale and stratum oriens in the CA3 and CA1 regions of the hippocampus. They were rare in the molecular layer of the dentate gyrus, in the stratum radiatum and in the stratum lacunosum-moleculare of the hippocampus. PV-I axon terminals were restricted to the granule cell layer, the stratum pyramidale and the immediately adjoining zones of these layers. Almost all PV-I neurons were also GAD immunoreactive (GAD-I), whereas only about 20% of GAD-I neurons also contained PV. The percentages of GAD-I neurons which were also immunoreactive for PV were dependent on the layer in which they were found; i.e. 40-50% in the stratum pyramidale, 20-30% in the dentate granule cell layer and in the stratum oriens of the CA3 and CA1 regions, 15-20% in the hilus and in the stratum lucidum of CA3 region and only 1-4% in the dentate molecular layer and in the stratum radiatum and the stratum lacunosum-moleculare of the CA3 and CA1 regions. PV-I neurons are a particular subpopulation of GABAergic neurons in the hippocampal formation. Based on their morphology and laminar distribution, they probably include basket cells and axo-axonic cells.

An immunohistochemical study of pro-somatostatin-derived peptides in the human brain

The distribution of pro-somatostatin-derived-peptide-positive profiles was examined by indirect immunohistofluorescence in nine post-mortem human brains (age 58-73 years). Three specific antisera were used for this study which recognize, respectively, somatostatin-28, somatostatin-28 (1-12) and somatostatin (1-14). Pro-somatostatin-derived-peptide-positive immunoreactive profiles were observed throughout the neuraxis. Cell bodies were found within archeo-, paleo- and neocortical areas, the subcortical white matter, in the nucleus accumbens, caudate nucleus and putamen, as well as in the hypothalamus, the reticular thalamic nucleus and the reticular formation of the brainstem. Fibers and terminals were seen in the same areas as well as in various thalamic nuclei, in the brainstem and spinal cord. Pro-somatostatin-derived-peptide-positive fibre tracts include the bed nucleus of the stria terminalis, the diagonal band of Broca, the stria medullaris, the inter-thalamic adhesion, the posterior commissure and the spinothalamic tract. Furthermore, differences between human and animal brains were noted and some somatostatin systems reported which may be implicated in certain human neuropathological states.

Co-localization of neuropeptide tyrosine and somatostatin immunoreactivity in neurons of individual subfields of the rat hippocampal region

The co-localization of neuropeptide tyrosine (NPY) and somatostatin (SOM) in rat hippocampal cells was studied in double labelling experiments using a combination of antibodies against the two peptides on the same tissue section. The individual hippocampal subfields show large variations in the relative number of NPY- and SOM-immunoreactive (-i) neurons. While the entorhinal area is far richer in SOM as compared to NPY-i cells, NPY-i cells predominate in all subfields (e.g. regio superior, regio inferior) of Ammon's horn. Co-localization of both peptides in single neurons was highest in regio inferior and in the area dentata and lowest in the retrohippocampal structures. In the dorsal hippocampus, the number of SOM-i cells containing NPY-i was higher than the number of NPY-i cells containing SOM-i. This pattern was reversed in the retrohippocampal region. At ventral levels the incidence of colocalization of NPY- and SOM-i in single cells increased in all hippocampal subfields.

Cholinergic innervation of hippocampal GAD- and somatostatin-immunoreactive commissural neurons

This study describes the cholinergic innervation of chemically defined nonpyramidal neurons in the hilar region of the rat hippocampus. Cholinergic terminals were identified by immunocytochemistry employing a monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme, and the avidin-biotin-peroxidase (ABC) technique. Nonpyramidal neurons in the hilar region were characterized by immunostaining with antibodies against glutamate decarboxylase (GAD), the gamma aminobutyric acid (GABA)-synthesizing enzyme, and somatostatin (SS). The immunoreactivity to these antibodies was detected by using biotinylated secondary antibodies and avidinated ferritin as an electron-dense marker. This electron microscopic double immunostaining procedure enabled us to demonstrate that immunoperoxidase-labeled ChAT-immunoreactive terminals established symmetric synaptic contacts on the ferritin-labeled GAD- and SS-immunoreactive hilar cells. In additional experiments at least some of the GAD- and SS-immunoreactive hilar neurons were further characterized as commissural neurons by retrograde filling with horseradish peroxidase (HRP) following an injection of the tracer into the contralateral hilus. From these triple labeling experiments, we concluded that at least some GABAergic and somatostatin-containing neurons in the hilar region, which are postsynaptic to cholinergic terminals, project to the contralateral hippocampus. Together with previous studies on the cholinergic innervation of the hippocampus and fascia dentata, our present results thus demonstrate that different types of hippocampal cells, including GABAergic and peptidergic commissural neurons in the hilar region, receive a cholinergic input.

Somatostatin immunoreactive neurons in the human hippocampus and cortex shown by immunogold/silver intensification on vibratome sections: coexistence with neuropeptide Y neurons, and effects in Alzheimer-type dementia

The distribution of somatostatinlike immunoreactivity was studied in the hippocampal formation, retrohippocampal region, and temporal cortex in the human brain. Tissues from surgical biopsy and postmortem cases were used, and the immunogold/silver method on vibratome sections was introduced for routine applications in conjunction with primary antisera that recognise somatostatin-14 or somatostatin-28. Somatostatin-28 antisera readily stained numerous neurons, dendrites, and extensive axonal networks throughout the hippocampus and neighbouring cortex. Liquid phase absorption provided controls for specificity. The most prominent accumulations of somatostatin immunoreactive neurons and axons occurred in the hilus of the area dentata, in CA1, and in the entorhinal and perirhinal cortices. Axonal plexuses occurred throughout the hippocampal subfields but were particularly dense in those regions rich in somatostatin neurons. The distribution of somatostatin immunoreactive neurons and fibers parallels the distribution of neuropeptide Y (NPY) neurons and fibers in the hippocampus and cerebral cortex to a remarkable extent. Double labelling experiments with antisera against neuropeptide Y and somatostatin indicate a considerable frequency of coexistence of the two peptides in single neurons, particularly in large multipolar cortical neurons and also in the small bipolar white matter neurons. Regional variations exist in the amounts of coexistence found in the hippocampal subfields; somatostatin-NPY coexistence is particularly high in the hilus of the area dentata, the subicular complex, and the deep layers of the entorhinal and perirhinal cortices. In the hippocampi and temporal cortices in cases of Alzheimer-type dementia compared to those of age-matched control brains, there is a significant to severe loss of somatostatin immunoreactive neurons and axons. This loss is most severe in those regions with the highest indices of neurofibrillary tangles and neuritic plaques-the hilus of the area dentata, CA1, and the entorhinal and perirhinal cortices. Surviving somatostatin neurons are distorted with short dendrites and truncated axons. Neuritic plaques identified on double label experiments with thioflavin include somatostatin axons but not neurons.